This invention relates to the art of sterilization, and more particularly to a new and improved sterilization method and apparatus employing ultraviolet light.
Traditionally, ultraviolet sterilization or germicidal radiation is accomplished by the passage of an electrical discharge through a low pressure mercury vapor and emitted at the 253.7 nanometer range. At this range, ultraviolet light has the ability to inactivate microbial forms. The amount of ultraviolet energy required to kill microorganisms is the product of time and intensity and is measured in microwatt seconds per square centimeter. Laboratory studies indicate that 8,000 microwatt seconds per square centimeter is sufficient for a 90 percent inactivation of most viruses and bacteria. Surviving microorganisms are left in a weakened state, interfering with replication and increasing their susceptibility to other inactivation methods including heat. This may be termed a static sterilization method, meaning only the microorganisms in direct reception of the ultraviolet light on the material surface are inactivated. Viruses and bacteria shielded by a continuously forming oxide layer, commonly associated with commercially pure titanium and titanium alloy instrumentation and implants, remain active. This microorganism protection from ultraviolet light is traditionally called a "screening effect". In addition to oxide layers, agglomerates, serum, blood, or even other cells may produce the shield, shadow zone, or screen effect. Thus, sterilization, using ultraviolet light in the traditional method, is very limited and unreliable in clinical application.
In recent times the phenomenon of surface energy activation has been the subject of various studies. These have involved examining biological films on material surfaces and their relationship to bioadhesion or biocompatability. Bioadhesion is essential to a successful osseointegrated bone implant. Studies over the years have encompassed sterilization, contaminants, critical surface tension, and the radio frequency glow discharge apparatus. Briefly findings from those studies are: bioadhesion is enhanced by a clean or surface energized" and sterilized material surface. Clean or "surface energized" means that a material surface is free of contaminants, agglomerates, and any oxide layer. Hence, the metal or material surface is bare or naked and very reactive to the surrounding environment.
Radio frequency glow discharge apparatus has been utilized in experiments for study of surface energy activation. The material's critical surface tension is changed thereby making it surface energy activated. To accomplish this surface energy activation on a specimen, the treatment requires the impact removal of an contaminant layers by the violently moving ionized gas particles within a chamber, and/or the microcombustion leading to complete conversion of the detached and contaminant layer matter to a gaseous form which is evacuated through a chamber exhaust. Two important points must be noted with respect to radio frequency glow discharge. First, surface energy activation or cleaning a material surface does not mean sterilization. Second, the material surface originality should not be changed, altered, or destroyed.
It would, therefore, be highly desirable to provide an ultraviolet sterilization method and apparatus which provides dynamic sterilization of a material surface and an increase in the critical surface tension of the material surface thereby inducing surface energy and increased bioadhesion.